In the spinning process, to produce a yarn of good quality, it is important to remove short fibers which are mixed in amounts not less than several percent in a mass of fibers used as raw material and to form a bunch of fibers which are as parallel as possible. The most common means for removing short fibers that is now in use in mechanical means such as extracting or combing action on fibers or a bunch of fibers gripped at one of their respective ends as in a carding or combing machine.
Besides the mechanical means described above, a method using static electricity is proposed in the June 1966 issue of the Textile World magazine. This utilizes a non-uniform electrostatic field; one of the opposed electrodes is shaped in the form of a planar surface and the other in the form of a curved surface which is a part of an oval, and these electrodes are disposed so that the distance therebetween gradually changes. The potential across the two electrodes linearly changes in reverse proportion to the distance between the electrodes.
In actual operation of such means utilizing static electricity, individual fibers are fed to a place between the electrodes where the intensity of the electrostatic field is lowest. As a result, these fibers are arranged along the direction of the force between the electrodes and are attracted toward a place of greater electrostatic field intensity. In this case, longer fibers are moved faster than short fibers toward said place of greater electrostatic field intensity. Short fibers are not attracted toward said place of greater electrostatic field intensity so easily as longer fibers and instead they remain in a place of less electrostatic field intensity for a long period of time. This principle makes it possible to separate fibers according to their lengths and to remove short fibers between the electrodes.
In the case of mechanical means among said conventional means for removing short fibers from a mass of fibers, breaks of fibers easily take place; thus, at the same time as short fibers are removed, new short fibers and naps are formed. Therefore, it is very difficult to reduce the short fiber content to less than a certain value. Other problems are that the amount of short fibers to be removed increases and that hooks form on fibers, thus detracting from the parallelism of fibers. Further, in the case of electrostatic means, short fibers tend to remain in a place of less electrostatic field intensity for a long period of time and short fibers lingering between the electrodes gather together and are connected in long-fiber form, sometimes moving toward long fibers; thus, there is a problem that the efficiency of removal of short fibers not satisfactorily high.